External cavity laser (ECL) technology is a robust solution for achieving interferometric sensing and/or other applications, including, but not limited to, distributed structural monitoring, military surveillance, seismic monitoring, telecommunications, data communications, etc. Traditional bulk-optics-based ECLs are prohibitively large in size, and may not be suitable for applications that require a compact device footprint. Semiconductor-based devices offer the advantage of smaller size and lower power consumption. Compared to other existing semiconductor-based interferometric sensing solutions, such as, systems using Distributed Feedback (DFB) lasers, ECL technology provides significantly narrower linewidth and lower phase noise. Hybrid ECLs based on fiber Bragg gratings (FBGs) may offer comparable narrow linewidth as semiconductor ECLs, but suffer from sensitivity to vibrations, and are relatively expensive to implement. It is to be noted that both waveguide Bragg grating based ECLs (such as the planar devices manufactured by Redfern Integrated Optics, Inc., Santa Clara, Calif., described further herein) and fiber Bragg grating based ECLs are semiconductor-based and hybrid, the difference being the embodiment of the waveguide: planar vs. fiber.
Planar lightwave circuits (PLCs) are photonic devices that are made using at least some of the standard semiconductor batch-fabrication techniques to achieve cost-effective volume production. Semiconducting materials and other structural or functional conducting or non-conducting materials are used to fabricate a planar device that is easy to integrate with other planar photonic or other devices. PLCs are much easier to package using industry-standard packages, such as, a 14-pin butterfly package, typically used for telecommunication devices.
What is needed is a low phase noise narrow linewidth external cavity laser that is compact and less power consuming, manufactured using cost-effective PLC methods, and is less susceptible to environmental variations.